1. Field of the Invention
The present invention relates to a process for producing a ceramic reinforced with fiber useful as materials for heat-resistant parts requiring high thermal durability such as gas turbine members (combustor and the like), nuclear fusion furnace walls, space system members (tiles for space return craft and the like); materials for structural members requiring high strength and rigidity such as aeroplane members and internal combustion engine parts; and various slidable parts.
2. Description of the Related Art
Development of high temperature structural materials is an indispensable technical requirement for improvement of members such as those for gas turbines, nuclear fusion furnaces, aerospace system and the like. These structural members are inevitably susceptible to high thermal load and thermal impact, and therefore, required to be structured with a material having excellent high temperature strength and thermal impact resistance.
A great interest has been directed to ceramics as high temperature materials, but the ceramics alone are brittle enough to have a low reliability and do not satisfy the above requirements for high temperature structural materials, which discourages the ceramics to put in practical use.
An attempt has been made to overcome the above difficulties by developing a composite material comprising a matrix having reinforcing fibers dispersed therein. For the reinforcing fibers light weight inorganic fibers having thermal durability (ceramic fibers) are suitable in view of the objects and applications of the composite materials. Some fiber reinforced ceramics have been proposed which have mostly a composite structure comprising a matrix having starting short fibers dispersed therein. However, the short fibers are liable to scatter into air in the process for production thereof causing serious problems from the standpoints of safety and environmental health hazards.
On the other hand, attention has been focused to a technique of dispersing nano-sized particles in a matrix in to improve the strength of the ceramics. There is, however, a problem that the necessity of using the nano-sized particles limits starting materials and adds to cost.
In order to use ceramics as high temperature structural materials, it is indispensable to enhance their reliability which requires a compatibility of high strength and high toughness. Specifically there are desired such materials as exhibiting non-linear fracture configuration which is capable of suppressing propagation of cracks, thereby inhibiting abrupt destruction. As means of achieving such materials one may make mention of a process for reinforcing ceramics by forming a composite of the ceramic matrix with short inorganic fibers as reinforcing material as well as a process for dispersing nano-sized particles in a matrix to be reinforced.
The reinforcement of composite ceramic matrix with inorganic fibers as reinforcing material tends to increase deficiencies such as stress concentration at ends of the fibers which may cause reduction in strength property for the structure where only short fibers are dispersed in the ceramic matrix. For the composite structure, therefore, such a structure as having long continuous fibers oriented in a matrix is desired.
The orientability of reinforcing fibers has fundamentally a great influence on the properties of resultant composite materials. For this reason, the orientability of fibers should be taken into consideration and controlled depending upon the application and desired characteristics of the resultant composite materials. Dispersing uniformly short fibers of a few micrometers in diameter throughout a matrix may be technically difficult. The short fibers of a few micrometers in diameter are apt to scatter into air and may adversely affect human body by aspiration and the like. Therefore, there is a need of a method without using short fibers as starting material.
On the other hand, the dispersion of nano-sized particles requires the use of nano-sized raw materials which in turn limits raw materials to be used, resulting in a sintered body in the form of restricted dispersion. Moreover, the raw materials must be reduced in size causing a problem of high costs so that there is a need for a method of dispersing nano-sized particles, other than the conventional methods.